AMBLYGONITE, a mineral usually found as cleavable or columnar, and compact masses; it is translucent and has a vitreous lustre, and the colour varies from white to pale shades of violet, grey, green or yellow. There are good cleavages in two directions. The hardness is 6 and the specific gravity 3·0. The mineral is thus not unlike felspar in general appearance, but it is readily distinguished from this by its chemical characters, being an aluminium and lithium fluophosphate, Li(AlF)PO4, with part of the lithium replaced by sodium and part of the fluorine by hydroxyl. Crystals, which are rarely distinctly developed, belong to the anorthic system, and frequently show twin lamellae.
The mineral was first discovered in Saxony by A. Breithaupt in 1817, and named by him from the Greek ἀμβλύς, blunt, and γωνία, angle, because of the obtuse angle between the cleavages. Later it was found at Montebras, dep. Creuse, France, and at Hebron in Maine; and on account of slight differences in optical character and chemical composition the names montebrasite and hebronite have been applied to the mineral from these localities. Recently it has been discovered in considerable quantity at Pala in San Diego county, California, and at Cáceres in Spain. Amblygonite occurs with lepidolite, tourmaline and other lithia-bearing minerals in pegmatite-veins. It contains about 10% of lithia, and, since 1886, has been utilized as a source of lithium salts, the chief commercial sources being the Montebras deposits, and later the Californian. (L. J. S.)